1,720,990 research outputs found
PEM fuel cell system analysis for grid connected applications
No full textL'incremento delle sorgenti ad energia rinnovabile porterà un grande cambiamento sulla rete elettrica nazionale, la quale dovrà operare in modo intelligente per gestire la fornitura di molti produttori di energia distribuita e per compensare l'imprevedibilità delle rinnovabili.
Tuttavia, per poter far ciò, le reti elettriche del futuro necessitano di generatori distribuiti capaci di assicurare servizi quali l'inseguimento del carico, l'accumulo di energia, la compensazione dei disturbi e che abbiano un effetto mitigante sui picchi di carico e/o di generazione.
I sistemi a celle a combustibile, specialmente quelli alimentati ad idrogeno, hanno raggiunto considerevoli target in termini di prestazioni in condizioni di laboratorio. Combinando alta efficienza ed un comportamento dinamico veloce (disponibilità di potenza immediata su richiesta), anche a carichi parziali e con piccole taglie, i sistemi a cella a combustibile di tipo PEM sono sempre di più analizzati nell'ottica del loro impiego nelle nascenti reti di potenza.
Lo scopo di questo lavoro è mostrare le attuali performance delle fuel cell, il loro comportamento durante il funzionamento con la rete elettrica ed, in particolare, i fenomeni relativi alla degradazione dei materiali che possono verificarsi in questo tipo di applicazioni.
Dapprima l'attività di ricerca è stata indirizzata allo sviluppo di un sistema da 5 kW di tipo PEM, considerando le procedure di start up e di warm up, l'analisi del comportamento dinamico in funzione della variazione della temperatura e del carico elettrico. Conseguentemente, alcuni test sono stati condotti sia su sistemi che su monocella in modo da poter confrontare le prestazioni in caso di carichi in corrente continua ed alternata.
Infatti, la potenza in reti monofase contiene una fluttuazione sinusoidale a bassa frequenza che procura un ripple sulla corrente di uscita dello stack. I test hanno mostrato la degradazione del materiale del catalizzatore dovuta a questo tipo di dinamica.An increase in renewable energy sources (RWE) will bring about a great
change in the national electric grid, which will operate intelligently (smart grid) in
order to manage the supply of several energy producers and to cover the
unpredictability of RWE [1].
Nevertheless, in order to become smart, the future electrical networks need
active distributed units able to assure services like load following, back-up
power, power quality disturbance compensation and peak shaving.
Fuel cell systems, especially those fed with hydrogen, have reached
considerable performance targets in laboratory conditions. Combining high
efficiency and fast regulating behaviour (power on demand), even at partial loads
and on small size units, PEM fuel cell systems are more and more investigated as
components of the incoming power networks.
The aim of this work is to highlight the fuel cells actual performances, their
behaviour during grid connected operation and, particularly, the phenomena of
materials degradation that can appear in these applications.
At first, the research activity was addressed to the investigation on a
developed 5 kW PEM fuel cell system, including the start-up and warm up
procedure, the analysis of the dynamic behaviour linked to temperature and load
variations.
Accordingly, tests were conducted both on fuel cell systems and single cells
in order to compare the performances evaluated with dc and ac loads.
In fact, power drawn by single phase grids contains a low frequency
sinusoidal fluctuation that brings a large ripple on the stack output current. The
tests on single cells have determined the degradation occurred on catalyst material
due to the effect of this kind of dynamic loads
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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